1. Field of the Invention
Embodiments of the invention generally relate to a temperature controlled lid assembly for a processing chamber and a method for depositing tungsten-containing materials on a substrate by vapor deposition processes.
2. Description of the Related Art
Modern integrated circuits contain large numbers of transistors. These transistors are generally field effect transistors that contain a source region and a drain region with a gate electrode located in between the source and drain regions.
A typical gate structure contains a thin polysilicon electrode that lies on top of a thin layer of gate oxide such as silicon oxide. The gate electrode and gate oxide are formed between semi-conducting source and drain regions, that define an underlying well of p-type or n-type silicon. The source and drain regions are doped opposite to the well to define the gate location, a layer of insulating material such as silicon oxide, silicon nitride, or silicon oxynitride is deposited on top of the source and drain regions and an aperture or via is formed in the insulating material between the source and drain regions. The gate structure within the via contains a thin oxide layer, a polysilicon layer and a metal plug. The metal plug is typically formed by vapor depositing a metal such as tungsten on top of the polysilicon gate electrode. To complete the connection, the silicon then is caused to diffuse into the tungsten during a thermal annealing process forming a layer of relatively uniform tungsten silicide as the connection to the gate electrode. Without annealing, the silicon will ultimately diffuse into the tungsten forming a non-uniform layer of tungsten silicide.
A gate electrode having an electrical connection made of pure tungsten would be more desirable than a tungsten silicide electrode since tungsten has a lower resistivity than tungsten silicide. Unfortunately, silicon diffuses into the tungsten forming tungsten silicide. The diffusion can be prevented by depositing a layer of tungsten nitride as a diffusion barrier between the tungsten and the silicon. Tungsten nitride is a good conductor as well as an excellent diffusion barrier material. Such a barrier layer is typically formed by reducing tungsten hexafluoride (WF6) with ammonia (NH3) in a chemical vapor deposition (CVD) process or an atomic layer deposition (ALD) process.
Unfortunately, the above described process results in the formation of contaminant particles in the form of solid byproducts. These byproducts include ammonia adducts of tungsten hexafluoride ((NH3)4.WF6), ammonium fluoride (NH4F), and other ammonium complexes. Many of these particles become attached to the interior of the deposition chamber. During temperature fluctuations within the chamber, the deposits flake off the walls and contaminate the wafer. Further, the tungsten nitride that is deposited using the above described process has a polycrystalline structure in which there are many grain boundaries. As a result, the diffusion barrier properties of the tungsten nitride are compromised. In addition, tungsten nitride films deposited by the traditional method tend not to adhere very well to the substrate upon which they are deposited.
Therefore, there is a need for an apparatus and a process for depositing tungsten-containing materials, wherein a tungsten precursor may be flowed with or exposed to another reagent without contaminating the processing chamber or the substrate surface.